In the earliest days of cinema, the scariest, terrifying, most unimaginably bloodcurdling thing on-screen was a simple train. The 1895 silent film “Arrival of a train at La Ciotat” is said to have sent audiences screaming for the exits, fearing they’d be run over.

The point is, what’s considered scary has evolved.

“Every decade, there’s a new group of filmmakers trying to top the previous decade,” says Brad Miska, editor-in-chief of horror site Bloody Disgusting.

From the 1930s through the ’50s, monster movies were often the frights of choice. In the 1970s, it was all about cannibalistic hill folk. The 1980s were an era of celebrity killers, such as Jason and Freddy.

In the aughts, torture porn, with “Hostel” and its endless rip-offs, was all the rage. Less so now.

“It got to a point when super-gore pictures started coming out, and they were trying to hit you really hard with violent imagery,” Miska says. “People didn’t respond to that, so then we de-evolved with the ‘Paranormal Activity’-type stuff.”

But the popularity of the so-called “found footage” genre, epitomized by the Paranormal franchise and “The Blair Witch Project,” in which the movie’s characters appear to film themselves, may also be waning.“This found footage nonsense has been parodied and roasted so much, I’m pretty sure it’s on its way out,” says Chris Alexander, editor-in-chief of horror magazine Fangoria. “I hope so. I find it unimaginative.”

We may currently be in a lull between horror trends, waiting for the next big thing to emerge. When it does, one thing is certain: It will arise out of the indie world.

The big studios release a handful of horror films annually, but true aficionados look to low-budget indie films that often get negligible theatrical releases or go straight to DVD or video-on-demand.

“There’s a big divide right now, in that you have mainstream horror fans who aren’t solely focused on horror who enjoy ‘Paranormal Activity 4,’ then you have hard-core horror fans who are sick of those movies but still see [them] because they see everything,” Miska says.

“Hands down, the best stuff is from smaller, indie filmmakers,” says Richard Bates Jr., the writer-director of the just-released “Excision,” made for less than $1 million. “I watch five movies a week, and pretty much all the good stuff is independent makers.”

The plots of recent cult favorites cover all sorts of nightmares. “Excision” is about a delusional high schooler (AnnaLynne McCord) who longs to perform surgery on her sister to win her parents’ approval. “The Snowtown Murders” dramatizes the true story of Australia’s most notorious serial killers. “The Innkeepers” is about employees stuck in an old haunted hotel. In “Chained,” a demented cabbie kidnaps fares and holds them prisoner in his house.

The one element that remains consistent is a disquietingly gritty realism.

“If you see stuff the studios put out, they don’t feel dangerous, because it doesn’t feel like this could happen to you,” Miska says. “The indie stuff that hard-core fans enjoy is more visceral.”

“In today’s culture we’ve been desensitized,” says director James Wan, who made the original “Saw” (for which he mostly raised the meager budget himself) and the creepy “Insidious.” “We are still scared of monsters, but it’s how these monsters are portrayed.”

Wan says the key is relatability.

“That’s the most important thing,” he says. “If it’s too unreal, you’re too much removed from it.”

Wan’s next film, 2013’s “Conjuring,” will have an extra touch of authenticity, in that it’s based on real people and actual events. It follows demonologists Ed and Lorraine Warren as they investigate a haunted farmhouse.

“I don’t see ‘Conjuring’ as being any different from ‘The Social Network,’ ” Wan says. “That’s what makes it exciting. It’s a drama.”

In “Excision,” Bates added relatability by shooting the movie to look like a “Disney kid’s show,” as opposed to a horror film.

“It’s not made to look in any way like a horror film,” he says. “The horror is that this can happen in your own backyard.”

One trope that scared viewers then and still does now is zombies, driven, in part, by the success of “The Walking Dead” TV series.

“Zombies are still No. 1,” Alexander says. “There doesn’t seem to be any sign of them leaving us.” Next year, “World War Z” and an “Evil Dead” remake are scheduled to hit.

“This is your wife, your child and your grandma, and they’re back from the dead,” says Alexander, who also wrote and directed a vampire film called “Blood for Irina.” “Also, when you hug them, they’re going to eat you. It’s just horrible.”

True, though not as horrible as 2006’s “Snoop Dogg’s Hood of Horror.” That’s frightening for an entirely different reason.